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Mortgage Extra Payment and Interest-Saving Calculator — result sheet
Estimate how an extra monthly payment or one-time principal payment changes the payoff time and interest of a fixed amortizing loan.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Scheduled payment = P×r/[1−(1+r)^−n] for r>0, or P/n when r=0; each simulated period applies interest to the balance and sends the scheduled payment plus extra payment to principal, limited by the remaining balance.
This is a transparent fixed-rate amortization scenario. It compares the scheduled loan with a plan that applies a one-time principal reduction and an extra amount each month. It does not assume a country, lender, prepayment rule, recast, or penalty; the visitor must confirm how extra payments are applied by the servicer.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Current principal balance — currency units; minimum 0.01; maximum 1000000000000
- Annual interest rate — %; minimum 0; maximum 100
- Remaining scheduled months — months; minimum 1; maximum 1200
- Extra monthly principal payment — currency units/month; minimum 0; maximum 1000000000000
- One-time principal payment now — currency units; minimum 0; maximum 1000000000000
Worked example
| Input | Value |
|---|---|
| Current principal balance | 250000 |
| Annual interest rate | 5 |
| Remaining scheduled months | 300 |
| Extra monthly principal payment | 200 |
| One-time principal payment now | 0 |
The standard monthly payment is about 1,461.29; the extra-payment schedule finishes sooner and reports the simulated months and interest saved.
Assumptions and limits
- The loan is fixed-rate with monthly interest calculated from the entered annual nominal rate.
- The scheduled payment is recalculated from the current principal and remaining months for this model.
- The extra monthly amount is applied after the scheduled payment to reduce principal.
- The one-time payment is applied immediately before the simulated first period.
- No fees, taxes, insurance, late charges, or prepayment penalty are included.
- The lender applies extra money to principal and does not merely advance the next due date.
- The final period may be smaller than the regular payment because the balance cannot become negative.
- A zero rate is handled as straight principal divided by scheduled months.
- The result is a scenario estimate and not a payoff quote from a servicer.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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